Purification of tetraalkyl lead



United States Patent 3,359,291 PURIFICATION OF TETRAALKYL LEAD David G. Braithwaite, Chicago, and Lawrence L. Bott, Oak Park, Ill., assignors to Nalco Chemical Company, Chicago, Ill., a corporation of Delaware No Drawing. Filed Oct. 5, 1964, Ser. No. 401,636 9 Claims. (Cl. 260-437) This invention relates to a purification process, and more particularly to a process for separating a water insoluble ether from a water insoluble tetraalkyl lead compound.

Water insoluble ethers of glycols are frequently used in the manufacture of tetraalkyl lead compounds. Thus, one process for making tetraalkyl lead compounds involves electrolyzing an alkyl Grignard reagent in a solvent comprising a water insoluble diether of a glycol, using a lead anode, and recovering a water insoluble tetraalkyl lead compound from the spent electrolyte. In the recovery system it is highly desirable to separate the water insoluble ether from the water insoluble tetraalkyl lead compound so that the Water insoluble ether can be reused in the process and the Water insoluble tetraalkyl lead compound can be produced in as pure a form as possible. It is rather dificult, however, to separate the Water insoluble other from the water insoluble tetraalkyl lead compound.

One of the objects of the present invention is to provide a new and improved process for separating a water insoluble ether from a water insoluble tetraalkyl lead compound by a method other than distillation.

Another object of the invention is to provide a process of the type described which is relatively simple.

Still a further object of the invention is to provide a process of the type described which will reduce the cost of manufacturing tetraalkyl lead compounds. Other objects will appear hereinafter.

In accordance with the invention it has been found that a Water insoluble ether can be separated from a water insoluble tetraa'lkyl lead compound by extracting a mixture of said water insoluble ether and said water insoluble tetraalkyl lead compound with a solution of water (preferably at least 20% by Weight water) and an organic solvent which is soluble both in water and in said ether.

The invention is generally applicable to the purification of any mixture of a tetraalkyl lead compound and a water insoluble ether. Examples of such tetraalkyl lead compounds are tetramethyl lead; tetraethyl lead; mixtures of tetramethyl lead and tetraethyl lead; triethylmethyl lead; diethyldimethyl lead; and ethyltrimethyl lead and mixtures thereof with tetramethyl lead and tetraethyl lead.

Examples of water insoluble ethers are the dibutylether of diethylene glycol, the hexylethylether of diethylene glycol, the phenylethylether of diethylene glycol, the hexylethylether of triethylene glycol, and in general diethers of alkylene glycols which are normally liquid at 20 C. and in which the terminal ether groups consist of hydrocarbon radicals either straight chained or branched chained or cyclic connected through oxygen to a central chain which is the residue of a glycol or a polyoxyalkylene glycol wherein the hydrocarbon groups in the terminal ether radicals contain a total of at least eight carbon atoms and the glycol nucleus or the polyoxyalkylene gly- "ice col nucleus contains two to six oxygen atoms inclusive of the terminal ether oxygen atoms. Diethers of this type may be described by the following general formulae:

where the radicals R and R are hydrocarbon radicals containing a total of at least eight carbon atoms and at least one of them preferably contains at least six carbon atoms and the radicals R R R R and R are alkylene radicals containing two to six carbon atoms. The invention is of special value where the Water insoluble ether is a dialkyl ether of a polyoxya'lkylene glycol containing a total of eight to twelve carbon atoms in the alkyl groups and two to six oxygen atoms in the glycol, the alkylene radicals in the glycol containing two carbon atoms.

Examples of suitable extractants are solutions of water with methanol containing 20-45% by weight water, solutions of water with ethanol containing 2045% by weight water, solutions of water with gammabutylrolactone containing 2045% by weight water and solutions of water with acetone containing 20-45% by weight water. Two or more of these organic solvents can also be dissolved in water and used as an extractant but usually it is desirable to keep the solvent system as Simple as possible. It is believed that the presence of water in the extractant makes the tetraalkyl lead compound less soluble than the ether in the extractant solvent.

The ratio of water to organic solvent in the exractant is subject to variation depending upon the particular organic solvent, the ether to be removed, the alkyl lead com pound, and temperature but it is preferable to use a volume ratio of water to organic solvent within the range of 4:1 to 1:4. Excellent results have been obtained by using a major proportion of the organic solvent and a minor proportion of water, for example, parts by volume of methanol to 60 parts by volume of water.

The volume ratio of extractant to the solution containing tet-raalkyl lead which is to be extracted is also subject to variation but it is preferable to use a vol-ume ratio of extractant to such solution within the range of 1:5 to 5:1. Good results have been obtained by using a volume ratio of extractant to solvent solution of tetraalkyl lead of about 8:3.

The extraction is preferably carried out by mixing the water insoluble solvent solution of the tetraalkyl lead compound with the extractant solution at temperatures within the range of 10 to 50 C., thereafter permitting the liquid mixture to stand so that liquid layers form, and separating the extracting layer containing the organic solvent, water and the extracted ether from the residual layer containing the tetraalkyl lead and residual ether. Successive extractions are carried out with the residual layer being extracted by additional portions of the aqueous solution of the organic solvent until the desired amount of water insoluble ether has been separated from the tetraalkyl lead.

The invention will be further illustrated but is not limited by the following example.

Example A solution containing 7.3 grams of tetraethyl lead dissolved in a suflicient amount of the hexylethylether of diethylene glycol to give 30 cc. of solution was shaken in a stoppered separatory funnel with six successive 80 cc. portions of aqueous methanol composed of 100 parts by volume methanol and 60 parts by volume water. After each extraction the liquid mixture was permitted to stand so that liquid layers could form and the ether-methanolwater layer could be separated from the tetraethyl leadether layer. The volume of tetraethyl lead-ether layer was measured after each extraction and the results were tabulated as follows:

Residual tetraethyl lead- Extraction: ether30 cc. starting volume, cc. First 27 Second 18.5 Third 12.0 Fourth 8.5 Fifth 6.0 Sixth 5.5

After the sixth extraction, calculated on the basis of the tetraethyl lead having a density of 1.59, the remaining 5.5 cc. was composed of tetraethyl lead with a purity in excess of 90%.

In a similar manner, other tetraalkyl lead compounds can be separated from a water insoluble ether solvent, thereby avoiding the necessity of subjecting the tetraalkyl lead to distillation which is more costly and, in some cases, more hazardous.

The invention is hereby claimed as follows:

1. A process for separating a water insoluble ether from a water insoluble tetraalkyl lead compound which cornprises extracting a mixture of said water insoluble ether and said tetraalkyl lead compound with a solution of water and an organic solvent which is soluble both in water and in said ether.

2. A process as claimed in claim 1 in which said water insoluble ether is a diether of a polyoxyethylene glycol containing a total of at least eight carbon atoms in the terminal ether groups and two to four oxyethylene groups.

3. A process as claimed in claim 1 in which the tetraalkyl lead compound is tetraethyl lead.

4. A process as claimed in claim 1 in which the tetraalkyl lead compound is tetramethyl lead.

5. A process as claimed in claim 1 in which the volume ratio of said organic solvent to water is within the range of 4:1 to 1:4.

6. A process as claimed in claim 1 in which the volume ratio of extractant to said mixture of said water insoluble ether and said tetraalkyl lead compound is within the range of 1:5 to 5:1.

7. A process as claimed in claim 1 in which said organic solvent is a solution of methanol in water.

.8. A process as claimed in claim 1 in which said organic solvent is a solution in water of a compound from the group consisting of methanol, ethanol, gammabutyrolactone, and acetone.

9. A process for separating a water insoluble diether of a polyoxyethylene glycol containing a terminal ethylether group, a terminal hydrocarbon ether group having at least six carbon atoms and two to four oxyethylene groups from tetraethyl lead which comprises extracting a mixture of said diether and tetraethyl lead with an aqueous solution of methanol in which the volume ratio of methanol to water is Within the range of 4:1 to 1:4.

References Cited UNITED STATES PATENTS 2,275,151 3/1942 Kimberlin.

2,572,887 10/1951 Stanton 260437 2,782,918 2/1957 Christoffcl 260616 3,007,858 11/1961 Braithwaite 20459 3,116,308 12/1963 Linsk 260--437 3,155,602 11/1964 Linsk 204-59 3,164,537 1/1965 Linsk et a1 260437 X TOBIAS E. LEVOW, Primary Examiner.

H. M. S. SNEED, Assistant Examiner. 

1. A PROCESS FOR SEPARATING A WATER INSOLUBLE ETHER FROM A WATER INSOLUBLE TETRAALKYL LEAD COMPOUND WHICH COMPRISES EXTRACTING A MIXTURE OF SAID WATER INSOLUBLE ETHER AND SAID ETERAALKYL LEAD COMPOUND WITH A SOLUTION OF WATER AN AN ORGANIC SOLVENT WHICH IS SOLUBLE BOTH IN WATER AND IN SAID ETHER. 